The present invention is related to the field of temperature control devices. More specifically, the invention is a thermostat with a variable length contact gap.
Thermostats were well known devices which were used in controlling the temperature of an enclosed area. One particularly well known type of thermostat included a deformable element which deformed upon a change in temperature, such as a bimetal element. Attached to the deformable element was a movable contact, which moved when the deformable element deformed. A fixed contact was positioned near the movable contact such that when the deformable element deformed due to a decrease (or increase) in temperature, the movable contact and the fixed contact were put into contact and in the process completed an electrical circuit. By completing the circuit, a plant, which can be either a heater or cooler or both, could be actuated to raise or lower the temperature of the enclosed area.
As the temperature of the space controlled by the thermostat rose (or dropped), the deformable element would recover from a deformed state to a normal state. This would cause the contacts to be open. The change in temperature required to cause the contacts to cycle from closed to open, or open to closed is called the thermal differential. In order to maintain a comfortable temperature in the controlled space, the thermal differential must be kept small. This in turn dictates that the mechanical distance from contact open to contact closed, be kept small.
To keep the mechanical distance small, a backstop was installed into the thermostat. The backstop is positioned such that the movable contact moves between the fixed contact and the backstop and is placed in close proximity to the fixed contact.
A problem exists in that there is a requirement in European countries that there be a three millimeter gap between the movable contact and the fixed contact for the device to be acceptable as an electrical disconnect. Yet, such a large gap at all times would require that a large temperature differential be overcome before the fixed and movable contacts touched.
Thus, it is an object of the present invention to provide a thermostat with low thermal differential when cycling. It is a further object of the present invention to provide a thermostat which is acceptable as an electrical disconnect when the thermostat is off.